1. Field of the Invention
This invention relates to a crosslinked polyamide prepared by reacting a crosslinking agent with a polyamide synthesized from an amine, a polyamine, and an unsaturated lactone. Among other things, the crosslinked polyamide is useful as a coating for a substrate, and is particularly useful in medical applications as a substrate coating that accepts an overcoat of an antithrombotic agent.
2. Description of the Related Art
It is well known that the physical properties of an organic polymeric material can be altered by introducing specific functional groups into the polymer backbone. For instance, polymeric materials that can conduct electricity, that are magnetic, or that change some property such as color or refractive index under the influence of various external factors such as light, pressure, electric fields, magnetic field, pH changes, or temperature alterations have been prepared by adding functional groups to the polymer backbone. In all of these applications, one critical requirement is that some of the functional groups along the polymer backbone be aligned in a regular repeating fashion with very high density. Polymeric materials with very different properties can be made depending on the choice of the functional groups. Electron donor-acceptor pairs can be conductive or have optical properties that are influenced by electric or magnetic fields. An array of negatively charged groups is a typical arrangement sought for conducting organic polymers where the charge carriers are metal ions and protons. Hydrogels can be formed if charges are present. Materials with special conductive, magnetic or electro-optical properties can be fabricated from polymers having specialized aromatic main or side chains.
In the background section of PCT International Publication Number WO 00/17254, several methods for introducing side chains to a main chain of a polymer are discussed and critiqued. For instance, it is reported in this document that one strategy for introducing side chains to a main chain of a polymer is to add the side chains to the preformed main chain. It is noted however, that this is generally not satisfactory because of the lack of predictability and reproducibility of stoichiometry, under-derivitization for stearic reasons, difficulty in accessing the interior of the polymer, poor solubility of the polymer, and inefficient coupling reactions. It further reported in WO 00/17254 that an alternative method for introducing side chains to a main chain of a polymer is to attach the desired side chain to each monomer prior to polymer chain formation. It is stated that this method is generally more efficient but the subsequent coupling of the monomers often requires activating groups to be attached to one or both coupling sites.
WO 00/17254 provides one solution to the aforementioned problems associated with introducing side chains to a main chain of a polymer. In WO 00/17254, there is disclosed a process for synthesizing a novel polyamide from unsaturated lactones and amines. In the polymerization reaction, the condensation of an unsaturated lactone with a variety of monofunctional, bifunctional or polyfunctional amines is initiated by a Michael reaction and is followed by ring opening of the resulting substituted lactone to give a polyamide. The resulting polyamide has a regular, sequential alignment of side chains along the polyamide backbone. The polymerization process can produce cationic, anionic or neutral polymers depending on the nature of the side chain attached to the main chain of the polymer. It is reported that the side chains can be among other things: a very long alkyl chain which generates a bipolar structure; a molecular system with special electrical properties; a polyamine with metal complexation properties; or a carboxylate with cation exchange or capture properties. The disclosed process provides a good general method for the assembly of a continuous array of side chains along a polymer backbone in a quick and efficient manner, does not require activation of groups of the monomer, does not produce any by products that have to be eliminated, proceeds under mild conditions, is compatible with a large spectrum of functional groups including alcohols, acids, phosphate groups, sulfonates, nitrites, amides and amines, can be carried out in a wide variety of solvents from aprotic solvents to water, and uses renewable resources instead of materials derived from fossil fuels.
While the polymerization process described in WO 00/17254 provides one solution to the aforementioned problems associated with known methods for introducing side chains to a main chain of a polymer, there is one disadvantage with the polyamide produced by the process of WO 00/17254. Specifically, it has been discovered that in certain coating applications, such as the use of the polyamide as a non-thrombogenic coating for surfaces which contact blood in medical applications (see, for example, Example 26 of WO 00/17254), the polyamide forms a soft waxy coating on the substrate being coated. This soft waxy polyamide coating has a tendency to be partially or totally removed from the substrate when contacted with aqueous medium and with certain solvents. The coating may become completely displaced from the surface of the substrate being coated. In medical applications where complete coverage of the underlying substrate is critical (e.g., applications where the substrate surface contacts blood), a coating prepared using the polyamide disclosed in WO 00/17254 may not be acceptable.
Therefore, there is a need for a process for improving the physical properties of the class of polyamides disclosed in WO 00/17254 such that the polyamides adhere more reliably to substrate surfaces. Also, there is a need for a polyamide having improved physical properties compared to the class of polyamides disclosed in WO 00/17254.
The foregoing needs in the art are met by a polyamide material comprising a crosslinked chemical combination of (1) a polyamide of the formula: 
wherein n is between about 50 and 10,000, wherein each R is between 1 and 50 carbon atoms alone and is optionally substituted with heteroatoms, oxygen, nitrogen, sulfur, or phosphorus and combinations thereof, wherein multiples of the R are in vertically aligned spaced relationship along a backbone forming the polyamide, and wherein two or more of the R contain an amino group; and (2) a crosslinking agent containing at least two functional groups capable of reacting with the amino groups of the polyamide. In one embodiment of the invention, the crosslinking agent is selected from the group consisting of aliphatic isocyanate compounds having 2 or more xe2x80x94Nxe2x95x90Cxe2x95x90O groups, aromatic isocyanate compounds having 2 or more xe2x80x94Nxe2x95x90Cxe2x95x90O groups, and mixtures thereof. In another embodiment of the invention, the crosslinking agent is selected from the group consisting of aliphatic aldehyde compounds having 2 or more xe2x80x94CHO groups, aromatic aldehyde compounds having 2 or more xe2x80x94CHO groups, and mixtures thereof. In still another embodiment of the invention, the crosslinking agent is selected from the group consisting of phosphines having the general formula (A)2P(B) and mixtures thereof, wherein A is hydroxyalkyl, and B is hydroxyalkyl, alkyl, or aryl. In yet another embodiment of the invention, the crosslinking agent is selected from the group consisting of epoxy resins having more than one epoxide group per molecule, and mixtures thereof.
A crosslinked polyamide in accordance with the present invention provides improved physical properties over the polyamides disclosed in WO 00/17254. The crosslinked polyamide also has many practical applications. For example, the crosslinked polyamide is particularly useful as a coating for a substrate. In one coating application, the crosslinked polyamide is used to coat a polymeric substrate which may comprise a natural polymer such as cellulose, or a synthetic polymer such as polyethylene, polypropylene, polyvinyl chloride, polyurethane, silicone rubber or polytetrafluoroethylene. In another coating application, an antithrombotic agent (i.e., a material that inhibits thrombus formation), such as heparin, is bonded to the crosslinked polyamide coating to produce an article suitable for medical applications in which the article contacts blood. (As used herein, xe2x80x9cantithromboticxe2x80x9d and xe2x80x9cnon-thrombogenicxe2x80x9d refer to any material which inhibits thrombus formation on a surface.) In yet another coating application, the crosslinked polyamide is used to coat surfaces in order to suppress biofilm formation. In still another coating application, the crosslinked polyamide is used as a thin conductive film for electronic devices. Additionally, the crosslinked polyamide may be used to coat oil and gas lines.